This invention relates to an injection molding machine driven by electric drive means, and more particularly, to the machine which can be driven concurrently by two servomotors.
Generally, a mold clamping apparatus and an injection apparatus of an injection molding machine are driven by hydraulic drive means or electric drive means. However, as well known in the art of this field, the energy efficiency obtained by utilizing the hydraulic drive means is lower than that obtained by the electric drive means, and the quick response to the speed change of a piston, for example, attained by the former means is inferior to that attained by the latter means. Accordingly, in an injection molding machine, it is desired to utilize the electric drive means as a drive source for finely adjusting and quickly responding to the operation of the machine.
For example, in a case where the injection molding machine is operated by the hydraulic driving means, a hydraulic pump is driven by an electric motor to operate an actuator such as a hydraulic piston-cylinder assembly or a hydraulic motor. However, the energy efficiency attained by using the hydraulic piston-cylinder assembly or by using the hydraulic motor is 70-75% or 55-60%, respectively, with respect to the energy efficiency attained by using the electric driving means, thus being not effective. In addition, resolving powers of a flow rate adjusting valve and a pressure adjusting valve located in a hydraulic operating circuit are limited, so that a speed and a pressure controlled by these control valves are not changed or controlled quickly with high precisions.
On the other hand, the injection molding machines operated by the electric driving means of the type disclosed, for example, in Japanese Patent Laid-open Publication Nos. 62030/1983 and 179630/1983, can eliminate the defects or problems described above in connection with the hydraulic drive means. The injection molding machines of the type disclosed in these Japanese prior patents include only one electric drive means as a driving source, so that it is considerably hard to sufficiently drive or rotate a screw in a plasticizing process which is the most important operation in the injection molding system simultaneously with the control of the back pressure when the screw is driven backwardly. These rotating and controlling operations had to be carried out consecutively, not simultaneously, in the prior art technique, thus being difficult to effectively shorten the time of molding cycle. In addition, when it is required to concurrently or parallelly carry out two or more operations of a mold opening-closing operation, injection compression foaming operation, injection formation operation of a thermosetting resin, and the like are not parallelly carried out during the plasticizing process by driving two different drive means associated with an injection molding machine.